At present, changing the lift and timing of the valve train of an engine is time-consuming and expensive, requiring the services of a skilled mechanic or technician.
As with conventional camshafts, the camshaft of this invention has cams for operating the valve lifters for the intake and exhaust valves of the engine. However, in accordance with this invention, each cam has more than one lobe. Each cam could very well have more than two lobes, but the invention can just as well be described and illustrated where only two lobes per cam are employed. Only two lobes per cam are needed in the embodiment disclosed hereinafter, which is a camshaft capable of changing the lift and timing of the engine from a position suited for relatively low speed (city street) operation to a position suited for relatively high speed (highway) operation.
In the specific embodiment described hereinafter, the camshaft can be moved longitudinally between a position in which one lobe of each cam is in contact with a valve lifter and another position in which the other lobe contacts the valve lifter. The longitudinal shifting of the camshaft takes place while the camshaft is rotating and the engine is running. Each cam lobe has a base circle area and a nose and ramp area. The base circle areas of the two lobes on each cam are the same radius. For a given cam, the shift from one lobe to the other cannot take place when the valve lifter is on the nose or ramp area of one of the lobes because of the step involved. Shifting, therefore, takes place at the base circle area. This is accomplished by providing an overlap in the base circle areas of the two lobes of each cam, by proper spacing of the cams along the length of the camshaft, by proper lateral positioning of the valve lifters relative to the cams, and by careful timing of the camshaft shift.
It is an object of this invention to provide a variable camshaft having the attributes referred to above, which will improve engine economy, performance, reduce emissions over a wide range of driving conditions, and which is of relatively simple design and construction having only a few moving parts, and is rugged and dependable in operation.
Other objects, features and advantages of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.